Drilling muds



Patented Feb. 7, 1-939 DRILLING -MUDS William V. Vietti and Allen D. Garrison, Houston,

Tex., assignors to The Texas Company, New York, N. Y., a corporation of Delaware No Drawing.

This invention relates to drilling muds and particularly to the type of drilling muds containing substantial amounts of sodium silicate solutions. The invention contemplates the use of bentonite or bentonitic clays as weighting materials in such muds.

Drilling muds are almost universally used in the drilling of wells employed for tapping underground collections of oil, gas, brines and water. These muds fulfill various functions-the most important of which are to assist in the removal of cuttings from the wells, to seal formations of gas, oil and water which may be encountered at various levels, and to lubricate the drilling tools and the drill pipes which carry the tools.

These drilling muds in their simplest form consist of suspensions of clay in water. In those cases where the drilling mud is used for drilling gas formations, it is necessary thatthe. hydrostatic pressure of the'drilling mud more than counterbalance the gas pressure in the formation. In such casesit is customary to increase the weight per volume of the drilling mud by the addition thereto of materials having a high specific gravity, such as barytes, iron oxide or finely divided non-colloidal solids. Natural clays are usually notv suitable for this purpose since they consist of mixtures of gel-forming particles and non-gel-forrning particles, and the addition therefore of such natural clays means the introduction into the drilling mudof colloidal gelforming particles which may excessively increase the gelstrength 'and viscosity of the drilling mud.

In our co-pending application Serial No.

46,893, filed October 26, 1935, we have disclosed the preparation and use of drilling muds containing substantial quantities of commercial sodium silicate solutions (water glass), such drilling muds being especially adapted to the penetration of heaving shale strata. We have also disclosed. in another co-pending application, Serial No. 94,586, filed August 6, 1936, that such drilling muds may also be prepared to contain substantial amounts of certain water-soluble inorganic-salts togetherwith the sodium silicate solutions. We have discovered that bentonite or bentonitic clays may be added in a dry state to Application December 8, 1936, Serial No. 114,764

7 Claims (Cl. 255-1) of bentonite, as well as those clays which display the property of defiocculating in water. Although we are not certain of the reactions thattake place, we believe that the sodium silicate represses the peptizingof the bentonite and that the bentoniteparticles become'filmed over or impregnated with silica;-gel-, v:and "are thereby prevented from being converted into colloidal particles. -We believe that the reason for this is that bentonites displayta bufier action, since they tend to maintain the pH value of the aqueous medium in which they are placed at a pH value of from 7 to 9. Sodium silicate solutions have pH values in the neighborhood of 11.- Therefore, when the dry bentonite is placed in the solution of sodium silicate, the bentonite, because of its buffering action, reduces the pH value of the sodium silicate solution with] the result that silica gel is precipitated. Silica gel being deposited upon and in the particles of bentonite prevents the peptizing of the bentonite and prevents its becoming colloidally dispersed. It should be understood, however, that we do not desire to be limited by the foregoing theo-' retical explanation of our invention.

The sodium silicates which we propose to use in the practice of our invention are the commercially available water solutions of sodium silicate. They are placed on the market in water solutions at concentrations near the practical .limitofvi'scosity for the purpose of avoiding the expense of shipping unnecessary amounts of water. It is well known that these commercial sodium silicate solutions range in water content from' about 35% for sodium silicates having a molecular ratio of 1.5:1 up to, about for the sodium silicates having molecular ratios of 3.9:1. We appreciate that commercial sodium silicates are prepared by dissolving in water sodium silicates which are sometimes spoken of in the art as sodium-silicate glass. In the practice of our invention we contemplate the use of commercial sodium silicate solutions without regard to their method of preparation.

In the practice of our invention we use sodium silicates in which the-molecular ratio of silica to sodium oxide is greater than 1 and, preferably, sodium silicates in which the ratio of silica to sodium oxide falls within the range of from 1.1:1 up to 3.9:1. Our invention may be prac-' ticed by using solutions of sodium silicate consisting essentially of sodium silicate and water or dispersions of finely divided solids in aqueous solutions of sodium silicate. We have disclosed filed August 6, 1936, that drilling muds adapted for drilling heaving shale containing sodium silicates will more eiiectively perform their functions it there are added to the sodium silicate solutions certain inorganic salts, namely, the sodium and potassium thiocyanates, chlorates,

iodides, nitrates, bromides, chromates and chlorides.af 1:In-.di spersions containing these salts we contemplate the use of a quantity of'salt ranging in amount'irorn about 2% by weight of the aqueous medium up to the saturation point of a dissolved constituent. In accordance with the present invention, bentonites may be used as weighting materials in any of the sodium silicate the desired viscosity and other characteristics.

As opposed to this practicerwe propose to add the bentonite in dry, pulverulent form to thesodlum silicate type drilling mud, whereby the bentonite serves as a weighting material and does not become colloidally. dispersed as in the prior art practice. I We do notintend to limit ourselves to the use of any particular quantity or bentonite and,

although we'contemplate thesuse of as much as 10% by'weight oi the dry material, we may employ both larger and smaller quantities.

We give herewith several examples which illustrate the practice of our invention. In these examples there were employed a natural Caliiorniabentonite which yielded a pH'value o! 9.2. I

in water suspension and a commercially available barium sulfate such as is generally used as a weighting material in the preparation of weighted drilling muds. I

1 Example 1 Four grams of bentonite were dispersed in water. To this dispersion there were added 25 grams of barium sulfate. added to bring the volume of the suspension to 80 cubic centimeters. To"the suspension there was then added 20 cubic centimeters'o! a sodium silicate inwhich the molecular ratio oi'silica to oxidewas about 2:1. When tested with a Stormer viscosimeter the suspension was found to havea viscosity corresponding to 24 centipoises.

Example 2 Example 3 I '20 a drilling mud comprising clay, barytes,

and 50% by volume of a sodium silicate in which the molecular ratio of silica to sodium oxide was about 2:1, there was added approximately 1.39%

by weight of bentonite. This" drilling mud had a viscosity 51 centipoises by the ,Stormer viscosimeter.

, 2,146,698 in our co-pe nding application Serial No. 94,586,

was'used in this example.

Bufllcient water was Example 4 A drilling mud containing the same quantities of constituents as the mud shown iii-Example 3 However, instead of adding the bentonite to the suspension of barytes, clay and sodium silicate solution the bentonite was originally dispersed in water so as to permit it to become deflocculated. This mud had a viscosityoi 101 centipolses when tested in a Btormer viscosimeter.

, Example 5 A drillingmudcontaining barytes, clay, water,

dispersed bentonite, chloride. potassium chloride, and" sodium silicate was prepared by dispersing 0.72%, by weight of bentonite in water and adding the dispersion to a drilling mud comprising-clay, barytes, sodium chloride. potassium chloride and about 33% by volume of a sodium silicate in which the molecular ratio'oi silica to sodium oxide washout-2:1. This drilling mud had a viscosity of approximately 21 centipoises by the Btormerr viscosimeter.

Example 6 with the exception that the bentonite was added last and in a dry form. It was-found that in order to obtain a viscosity of 21 'centipoises it was necessary to add 18 times as much bentonite'as in the case 01' Example 5 where the bentonite had been first dispersed in water.

The above examples clearly indicate that when bentonite is added in dry form to a' solutionoi sodium silicate or a suspension of which the aqueous phase contains sodium silicate that the bentonite serves as a weighting material and not as a colloidal suspending agent.

Obviously many modifications and variations of the invention as hereinbeiore set forth may be made without departing from the spirit and scope thereof and only such limitations should be imposed as are indicated in the appended claims.

We claim:

1. A drilling mud comprising bentonite in substantially undispersed state and 20% or more by' volume of sodium silicate in which the molecular ratio of silica to sodium oxide is greater than 1.

2. A drilling mud comprising bentonite in substantialy undispersed state and from 20 to 70% of sodium silicate in which the molecular ratio of silica to sodiuxri oxide is greater than 1. u

3. A drilling mud comprising 20 to 70% of sodium silicate in which the molecular ratio of silica to sodium oxide isgreater than 1 and to which has been added dry, pulverulent bentonite.-

4. In the art of drilling wells, the method comprising'introducing into the well a drilling mud containing 20% or more by volume of sodium silicate in which the molecular ratio of silica to sodium oxide is greaterthan 1, and controlling the density 01' said mud by the addition of dry,

pulverulent bentonite. A

5. A drilling mud comprising bentonite in substantially undispersed state, sodium silicate in which the molecular ratio of silica to sodium oxide is greater than 1, and at least one'salt selected from the group consisting oi the sodium and potassium thlocyanates, chlorates, iodides, nitrates, bromides, chromates and chlorides, the salt content'of the dispersion falling within the range of from 2% by weight of the aqueous medium up to the saturation value of a dissolved component.

e. A drilling mud comprising bentonite in substantially undispersed state, from 20 to 70% of chlorides, the salt content of the dispersion tailing withirr the range of from 2% by weight of the aqueous medium up to the saturation value of .a

a dissolved component.

7. Intheart oidrillingwellsthemethodcomprising introducing into the well a drilling mud sodiumoxide is greater than 1 at least one salt selected from the group consisting of the sodium and potassium thiocyanates, chlorates, iodides, nitrates, bromides, chromates and chlorides, the salt content'oi thedispersion tailing within the range of from 2% by weight of the aqueous medium up to the saturation value gt a dissolved component, and controlling the; density of said 10 mud by the addition of dry pulveruleni; bento'nite,

WILLIAM V. VIE'ITI. ALLEN D. GARRISON;

containing 20% or more by volume oi I silicate in which the molecular ratio of silica to 

